1. Field of the Invention
The present invention relates to a method of signal processing in a hearing aid system. The invention, more specifically, relates to a method of noise suppression in a hearing aid system. The invention further relates to hearing aid systems having means for noise suppression.
In the context of the present disclosure, a hearing aid should be understood as a small, microelectronic device designed to be worn behind or in a human ear of a hearing-impaired user. A hearing aid system may be monaural and comprise only one hearing aid or be binaural and comprise two hearing aids. Prior to use, the hearing aid is adjusted by a hearing aid fitter according to a prescription. The prescription is based on a hearing test, resulting in a so-called audiogram, of the performance of the hearing-impaired user's unaided hearing. The prescription is developed to reach a setting where the hearing aid will alleviate a hearing loss by amplifying sound at frequencies in those parts of the audible frequency range where the user suffers a hearing deficit. A hearing aid comprises one or more microphones, a microelectronic circuit comprising a signal processor, and an acoustic output transducer. The signal processor is preferably a digital signal processor. The hearing aid is enclosed in a casing suitable for fitting behind or in a human ear.
It is well known that people with normal hearing can usually follow a conversation despite being in a situation with several interfering speakers and significant background noise. This situation is known as a cocktail party environment. As opposed hereto hearing impaired people will typically have difficulties following a conversation in such situations.
2. The Prior Art
In the article by Allen et al.: “Multimicrophone signal-processing technique to remove room reverberation from speech signals”, Journal Acoustical Society America, vol. 62, no. 4, pp. 912-915, October 1977, a method for suppression of room reverberation, from the signals recorded by two spatially separated microphones, is disclosed. To accomplish this the individual microphone signals are divided into frequency bands whose corresponding outputs are cophased (delay differences are compensated) and added. Then the gain of each resulting band is set based on the cross correlation between corresponding microphone signals in that band. The reconstructed broadband speech is perceived with considerably reduced reverberation.
US-A1-20080212811 discloses a signal processing system with a first signal channel having a first filter and a second signal channel having a second filter for processing first and second channel inputs and producing first and second channel outputs, respectively. Filter coefficients of at least one of the first and second filters are adjusted to minimize the difference between the first channel input and the second channel input in producing the first and second channel outputs. The resultant signal match processing of the signal processing system gives broader regions of signal suppression than using Wiener filters alone for frequency regions where the interaural correlation is low, and may be more effective in reducing the effects of interference on the desired speech signal.
One problem with the above mentioned systems is that noise from interfering speakers is not efficiently suppressed.
It is therefore a feature of the present invention to overcome at least this drawback and provide a more efficient method for suppression of noise from interfering speakers.
Hereby speech intelligibility for the hearing impaired can be improved in the otherwise very difficult situation of following a conversation despite several interfering speakers.
It is another feature of the present invention to provide a hearing aid system incorporating means for suppression of noise from interfering speakers.